Aqueous resin adhesive composition having pre-bake resistance

Abstract

An aqueous adhesive composition, as for bonding nitrile rubbers to a metal substrate, has very good pre-bake resistance. The adhesive composition comprises a phenolic novolac or resole resin, chlorinated natural rubber, a reactive fillers, and precipitated silica. Utilization of the adhesive composition results in essentially failure of the nitrile rubber.

Description

The present invention relates to a water based dispersed adhesive which contains a phenolic resin, chlorinated natural rubber and unexpectedly has improved pre-baked properties when precipitated silica is utilized.Heretofore, phenolic resin compositions have been utilized for bonding rubber to metal. While solvent based systems have generally had good pre-bake properties, apparently no known aqueous system exists which has good bonding of a rubber such as a nitrile to a metal as well as good pre-bake resistant properties. U.S. Pat. No. 5,093,203 relates to a rubber-metal adhesive system which contains a primer component and an overcoat component. The primer component includes a polychloroprene compound, a phenolic resin, and a metal oxide while the overcoat component preferably contains a nitroso compound, a halogenated polyolefin, and a metal oxide or salt. When applied between a metal surface and a rubber substrate under heat and pressure, the adhesive system provides a flexible r...

AI Technical Summary

Benefits of technology

It should be noted that it is believed that the effectiveness of the present phenolic resin copolymer is based on the presence of the trihydroxy aromatic compound (the second phenolic component) in the copolymer, and therefore, the trihydroxy aromatic compound is an essential component of the copolymer. The first phenolic component of the copolymer may be a monohydroxy aromatic compound, a dihydroxy aromatic compound, or a combination thereof. However, the use of at least one dihydroxy aromatic compound in the first phenolic component of the invention has been shown to exhibit exceptional bonding ability (possibly due to the numerous hydroxy groups present in the resulting copolymer), and a dihydroxy aromatic compound is therefore particularly preferred for use in the first phenolic component of the invention.

As noted above, the aqueous rubber to metal adhesive compositions of the present invention have very good pre-bake resistance. Pre-bake resistance can be defined as a capability of tolerating a pre-bake cycle of about 3 or about 6 minutes and especially about 9 minutes at 380.degree. F. and still maintain the capability of providing approximately 100% rubber tearing bonds when used as an adhesive bonding nitrile rubber to a rigid substrate such as zinc phosphated steel during vulcanization of the nitrile rubber compound. That is, even though heated for up to 3, 6, or 9 minutes at 380.degree. F. before any cure of the nitrile rubber, after cure of the rubber, the adhesive does not fail but rather generally at least 80%, desirably at least 85% or 90% and preferably at least 95% or 100% of the nitrile rubber (bonds) tears during testing of the laminate. Pre-baked resistance is often very desirable since with regard to adhesive coated seals, adhesive movement is prevented when unvulcanized rubber moves across the pre-baked adhesive during a molding step. Another important advantage is that when loading molds which are preheated to a molding temperature of up to about 400.degree. F., adhesive coated inserts can be exposed to these temperatures for up to several minutes prior to rubber contact and cure initiation. The adhesive must resist pre-curing as a result of such heat exposure. Should the adhesive be pre-cured, the same will typically fail at the rubber-adhesive interface and not provide for desired rubber retention when destructively tested.

The nitrile rubber compositions of the present invention are generally conventional. The nitrile rubbers are made from a conjugated diene having from 4 to about 8 carbon atoms such as 1,3-butadiene generally in an amount of from about 60% to about 80% by weight with the remainder being the weight of the acrylonitrile content. Such rubbers are conventional an well known to the art and can be obtained from Zeon Chemicals Inc. of Louisville, Ky. The nitrile rubber can be sulfur cured, peroxide cured, or the like and can have a high or low modulus. Furthermore, the nitrile rubber can be hydrogenated or carboxylated, and made by emulsion polymerization. One of the advantages of the adhesive compositions of the present invention is that they effectively bond to wide variety of nitrile rubbers.

Problems solved by technology

While solvent based systems have generally had good pre-bake properties, apparently no known aqueous system exists which has good bonding of a rubber such as a nitrile to a metal as well as good pre-bake resistant properties.